FRANKFURT, Sept 20 (Reuters) - German drugmaker Bayer requested European approval for a contraceptive skin patch as it seeks to broaden its birth-control business and challenge Johnson & Johnson's Evra patch.

The hormonal contraceptive, to be produced for Bayer by Swiss company Acino, was shown to be effective with a good safety profile in clinical trials involving 4,200 women, Bayer said on Thursday.

It added that detailed results will be presented at the FIGO World Congress of Gynecology and Obstetrics in Rome in October.

The transparent patch, which Bayer says could generate annual sales of 250-500 million euros ($325-$650 million), is applied once a week either to the abdomen, buttocks or outer upper arm, where it delivers a steady dose of hormones through the skin.

If successful, Bayer's product would offer an alternative to J&J's Ortho Evra birth control patch, which is approved in North America and Europe.

U.S. drug advisers have, however, recommended that the label of Ortho Evra patch be simplified to better explain the risk of blood clots.

A spokeswoman said Bayer was in talks with the Food and Drug Administration over a possible filing also in the U.S.

Bayer, is one of the largest players in the $8 billion global market for hormonal birth-control pills, competing with J&J, Teva's Barr Pharmaceuticals and Ireland-based Warner Chilcott.

Its main oral contraceptive brand Yasmin has also been subject to controversy over health risks. Bayer has agreed to pay a combined $400 million to settle almost one third of about 6,000 legal claims in the U.S. that Yasmin caused blood clots.